1. Field of the Invention
The present invention relates generally to a carriage assembly for use with flexible magnetic disk drive systems and more particularly to a carriage assembly that utilizes a stepper motor and a voice coil motor to permit optical servo tracking in a high track density flexible magnetic disk drive system.
2. Description of the Prior Art
The track density of magnetic storage disks for conventional floppy disk drives is approximately forty-eight to one hundred thirty-five tracks per inch (TPI). In contrast, optical disk drives are capable of achieving track densities in excess of 15,000 TPI. These higher track densities are achieved through the use of closed loop optical servos that allow an optical read/write head to follow data track eccentricities caused by defects in the medium and by disturbances from outside forces. In rigid type magnetic disk drives, track densities of up to 1500 TPI are presently used. These drives commonly have multiple disks in which both sides are used for data. To achieve the high track density a dedicated surface of one of the disks is used for magnetic track servo information.
Various techniques have been reported for using optical means for acquiring track following servo information contained on a magnetic recording medium. For example, Ahn, et al., in U.S. Pat. No. 4,633,451, issued on Dec. 30, 1986, for "Optical Servo For Magnetic Disks", discloses the use of a laser diode to read track following servo information in the form of a plurality of spots contained in an optical layer positioned above a magnetic recording layer.
M. Johnson, in U.S. Pat. No. 4,558,383, issued on Dec. 10, 1985, for "Information Storage Disk Transducer Position Control System Using a Prerecorded Servo Pattern Requiring No Alignment With The Storage Disk", discloses a servo apparatus having a sensor for detecting a pattern of spots on a surface of an information storage medium. The spots comprise a dense array of substantially translation invariant marks and separate information recording tracks are detected by measuring the rate at which the spots are detected.
J. Cocke, et al., in U.S. Pat. No. 4,587,579, issued on May 6, 1986, for "System for Position Detection On A Rotating Disk", disclose a servo control system comprising a detector for reading a plurality of spiral radial-position-encoding patterns on a medium.
N. Koshino and S. Ogawa, in "Optical Method Of The Head Positioning In Magnetic Disk Systems", preprint from IEEE Transactions on Magnetics (1980), discloses an optical head for achieving track following servo control which is mounted on the head arm and which includes an LED light source and three optical fibers for delivering light to a medium. The medium comprises a plurality of circular optical tracks, dyed black, and located underneath a magnetic film.
In U.S. patent application Ser. No. 07/178,542, filed Apr. 7, 1988, an optical servo tracking head is disclosed for reading optical servo tracking information contained on magnetic media comprising nonreflecting servo areas situated around reflective land areas.
Related work has occurred in the laser video disk area, from which optical disks for digital data storage and the audio laser disk (CD) have evolved. Fundamentally, the optical servo information is inscribed and used in the same way for all these disks. A laser and associated optics positioned on a carriage assembly are used to acquire the optical servo information as well as to read data from the disk. Typically, CD disk drive systems utilize a flexure/voice coil design in the optical focus assembly.
T. Aihara, et al, in U.S. Pat. No. 4,092,529, issued May 30, 1978, disclose an optical detecting head suspended by resilient leaf springs or wires and driven by a magnet and coil means.
None of these techniques disclose a carriage assembly that can be used with a high track density flexible magnetic disk which utilizes magnetic data tracks and optical servo tracks.